JOURNAL OF CHEMICAL EDUCATION
AN AUTOMATIC LEVELING PYCNOMETER SHIRLEY A. BROWN and JAMES E. LAND Alabama Polytechnic Institute, Auburn, Alabama
IN recent investigation, in which a large number of density determinations of saturated solutions were required, the pycnometer illustrated in the figure
0 I
2tM
LLL
SCALE
proved to be quite advantageous. Its design is such that the major part of the pycnometer can be immersed in the constant-temperature bath during the filling and leveling operations. The capillary bore size was approximately one mm. The dimensions shown gave a bulb of approximately 30-ml. capacity. The size of part A could be varied, however, it is desirable to keep the neck long enough so that the capillary tip is at least one cm. above the major body of the liquid. Liquid is drawn into the pycnometer through tube C by applying suction to tube D. The successful operation of this device depends upon maintenance of the correct amount of suction. It was found that a vacuum of three cm. of mercury below atmospheric pressure gave optimum results. Since this requirement may vary with the nature of the capillary tip, it is best to maintain suction so that rapid dropping, but not a liquid stream, occurs from the capillary tip. A stream will cause bubbles of air to be trapped in the liquid. When the level of the liquid in part A is about one cm. above the tip of the capillary, tube D is opened to the air and gentle suction is applied to tube C. After liquid is no longer drawn up the capillary, and with suction still being maintained, part B is removed from part A . B is replaced with a ground-glass cap before rinsing, wiping, and weighing. The accuracy of measurement has been found to he of the order of 0.01 per cent.
